The present invention relates to a mine roof support for underground mine galleries, which comprises a sole plate adapted to rest on the floor of the mine gallery, a rear shield connected in the region of the lower end thereof by link means to the end of the sole plate which is directed away from the mine face, and which is connected by pivot means to a roof shield, intermediate the ends of the latter, in which the rear shield is at least indirectly supported by an extensible and collapsible prop.
The sole plate may be constituted by a single integral member or, for instance in order to adapt itself to an uneven floor of the mine gallery, it may also be constructed of two parallel elongated members extending in the longitudinal direction of the mine gallery and which are connected to each other for movement relative to each other. The rear shield and the roof shield have large areas and may be constructed of a plurality of parts. The link means between the rear shield and the sole plate are constructed in such a manner that the front edge of the roof shield, directed toward the mine face, may be moved closely adjacent to the latter so that mine roof portions which are newly exposed by a mining machine may be properly supported.
At least one, but usually two hydraulically operated props are provided in order to apply a supporting force for the roof and the piston rods of the props are connected to the rear shield, or the roof shield, respectively directly to the pivot means which connect the rear shield with the roof shield. The pivot means which connect the upper end of the rear shield to the roof shield is usually provided substantially midway between the opposite ends of the roof shield. However, a construction is also known in which the distance of the front end of the roof shield from the pivot means is slightly longer than the distance between the pivot means and the rear end of the roof shield.
Even though the above-described mine roof supports have proven satisfactory in principle, they have certain shortcomings, if the loading thereof by the roof of the mine gallery will produce unusual stresses on the different components of the mine roof support, which thereby considerably impair the stability of the latter and the possibility of its use. This will occur especially if the load acts closely adjacent to the front edge of the roof shield. Such loads will detrimentally influence the stability of the mine roof support to an increasing extent, the farther the pivotal connection of the prop or props to the roof shield, respectively to the rear shield, is shifted away from the mine face. One sided loading of the roof shield can also be observed, especially when the mine roof support is applied to a fold or an otherwise irregular mine roof. Diagonal loading of the mine roof support, which will detrimentally effect the proper operation thereof, may also occur when the mine roof is inclined relative to the sole of the mine gallery. Situations have also to be taken into account in which the portion of the roof shield, projecting from the pivot means forwardly towards the mine face is loaded less than the portion of the roof shield which projects rearwardly from the mentioned pivot means.
The above-mentioned loadings of a mine roof support can only be constrolled to a limited extent with an arrangement of the props at which only the roof shield or the rear shield is supported, respectively in which one or two props engage directly the pivot means between the roof shield and the rear shield. In all these cases the occurring loads or stresses can only be counteracted to a limited extent, because the engagement points of the props are arranged in such a manner that only one, maximally two of the possibly occurring types of loading are considered. This may result in damaging various parts of the mine roof support, with the resultant interruption of its operation. Even though it has already been tried, by mounting cylinder and piston means between the rear shield and the roof shield, to adjust the angle between the two shields, this arrangement requires additional expenditure without increasing the total supporting force of the mine roof support to thereby assure control of any of the aforementioned unusual loadings of the mine roof support.